Air-cooled spark plug



Jan. 10, 1950 1 A, BENSON 2,493,743

AIR-COOLED SPARK PLUG Filed Sept. l0. 1948 Inventor. "John ABenson,

casing I.

Patented Jan. l0, 1950 Ain-coo'Lnn. SPARK PLUG John A. Benson, Nahant,Mass., assignor General Electric Company, a corporation of New YorkApplication September 10, 1948, Serial No. 48,555

2 Claims. 1

This invention relates to electric igniters, and more particularly toelectric spark igniters subjected to high temperatures as in internalcombustion power plants.

The invention is well adapted for use in connection with spark plugs forthe combustors of gas turbine powerplants, and it is this application ofthe invention which I have elected specically to illustrate anddescribe. It is to be understood, however, that the invention is notlimited thereto necessarily but may be used also in rocket or reactiontype motors and other combustion apparatus.

Actual service experience has shown that thermal powerplants of the typedescribed are subject to serious limitations with regard to permissiblepower rating, operating temperatures,

service life of the igniting device, and the max-v imum interval betweenoverhauls because of the inability of the igniting device to withstandthe exceedingly high temperatures to which it is subjected during theoperation of such powerplants. Furthermore, because of high operatingtemperatures, it has not been possible to locate the igniter in the mostfavorable location for optimum ignition characteristics of thecombustor.

Accordingly, it is an object of this invention to provide a novel andimproved arrangement for cooling the ignlter.

It is also an object of the invention to prevent fouling of the igniterwhich may result from the deposition of unburned fuel or carbonizedparticles on the electrodes, insulator or other eX- posed parts of theigniting device, which might provide a current leakage path or otherwiseadversely effect ignition of the fuel by the spark.

Other objects and advantages will be apparent from the followingdescription taken in connection with the accompanying drawings, in whichFig. 1 is a view, partly in section, illustrating one embodiment of theinvention as applied to a gas turbine powerplant; Fig. 2 is an enlargedsec-. tional view of the arrangement shown in Fig. l; Fig. 3 is anenlarged sectional view illustrating a modied arrangement of theelectrodes; and Fig. 4 is another enlarged sectional view illustrating afurther modification.

Referring now to Figs. 1-3, an outer casing I denes an air supply space2, in which a cylindrical inner wall or linerf 3 is co-axiallysupported, as for example, by a plurality' of radially extending ns orbaflles 4. These ballles may be welded to the outer surface of liner 3and arranged to slide freely into the outer housing or The liner 3defines an velongated combustion space which is closed at one end by anend dome 5. The opposite end of the combustion space is open to permitthe discharge of the combustion products `to a suitable turbine (notshown). For the purpose of illustration, the combustion shown ls similarto that disclosed in the copending application of Anthony J. Nerad,Serial No. 750,015,1 filed May 23, 1947, and assigned to the sameassignee as the present application; but it should be noted that theinvention may be applied to other combustion devices of the general typedescribed.

The end dome 5 supports a fuel nozzle 8, which is preferably of a typewhich produces a conical spray of fuel particles, as indicated by thespray pattern 1. A conduit 8 serves to conduct fuel to the nozzle from asuitable fuel supply means (not shown). As is more particularlydescribed in the above-mentioned application of Anthony J. Nerad,combustion air under pressure is conveyed by means of a duct or airadapter 9 from a suitable compressor (not shown) to the air supply space2. This combustion 'air is admitted from the air supply space to thecombustionvor reaction space within liner I through a plurality ofspaced holes I 0.

In order to initiate combustion in the chamber, an igniting device inthe forni of an electrically-energized spark plug, Is provided. Sparkplug II may be supported on air adapter 9 by a mounting boss I2 in sucha manner that an end portion of the spark plug projects through the enddome and into the combustion chamber. The arrangement and proportions ofthis end portion of the spark plug is such that electrodes I3, I4 whichdenne the spark 'gap are located substantially in the normal path ofthe. conical spray pattern 1 of fuel particles issuing .rom the fuelnozzle 8. Surrounding an insulator I5 and the central electrode I3 ofthe spark plug is a cylindrical co-axially spaced metal sleeve I8forming an annular cooling air passage I1. An opening Il, Figures 1 and2, is provided in sleeve I6 in cooperative relation with the air supplyspace 2 and the cooling passage I1 to form a complete ow path for thecooling air around the insulator and the central electrode.

Still referring to Figures 1-3, the second igniter electrode I4 maycomprise a hollow tubular member bent or formed to any suitableconfiguration as illustrated in the drawings. One end of electrode I4 ismaintained in spaced relation with the central electrode I3 to define aspark gap of any desired value. Electrode I4 may be secured to theshroud or sleeve I6 by welding or ment is feasible because in theordinary operation of a combustor of the type described there is adenite pressure drop from the supply space 2 to the reaction spacewithin the liner 3. This pressure drop is therefore available to effecta flow of cooling air through opening I8 and cooling passage I1. Ofcourse, a separate auxiliary source vof cooling air at any desiredpressure may be employed if desired. It will also be obvious to thoseskilled in the art that since the total or the dynamic pressure of theair owing in the air supply space 2 and against the open end of member I4 will always be greater than the static pressure of the same air streamin the absence of any pressure conversion or diffusion process, there isa decrease in pressure from one end of member I 4 to the other in such adirection as to cause a ow of air through this member from the airsupply space 2 to the interior of the combustion chamber.

An important feature of the arrangement is that this flow of relativelycool air from hollow electrode I4 is discharged directly against theexposed end portion f the solid. central electrode I3. Thus the airissuing from electrode I4 as indicated by arrow I4a serves toeffectively cool the solid electrode I3 as well as to insulate thelatter so as to prevent the deposit of carbonized fuel particlesthereon. Obviously electrode I4 is cooled by virtue of theair flowingthrough it as indicated by arrow I4a. In addition, the air issuing fromthe open end of shroud I6, as indicated by arrows I6a, also tends toblow fuel particles away from both electrodes to prevent the deposit ofcarbonized fuel particles thereon.

A modied embodiment of the invention is illustrated in Fig. 3. Thisarrangement is similar to Fig. 2, but differs in that the discharge fromI electrode I4 is substantially coaxial with the axis of solid electrodeI3 and that the opposite end is arranged to face in the proper directionto receive substantially the full dynamic pressure from the air supplyspace as will be apparent from the drawing.

A further modification is illustrated in Fig. 4. The sleeve or shroud I6may be replaced by concentric spaced walls 20, 2l surrounding theinsulator I and the central electrode I3 and defining cylindricalco-axially spaced shroud means and forming annular cooling passages I1and 22. Walls 20, 2I may be welded to a supporting member 23 which alsoforms a closure for the upper portion of passage 22. The other end ofwalls 20, 2| are bent or formed to close the lower end of thecylindrical shrouds except for circular openings 24, 25 of equaldiameter which are provided in each of the walls 20, 2I concentric withcentral electrode I3. The diameter of openings 24, 25 is of such valueas to define annular spark gaps between the central electrode I3 andwalls 20, 2| of any desired value.

Openings 26, 21 are provided in walls 20, 2I, respectively, to admitcooling and insulating air to passages I1 and 22. Ordinarily opening 21will be made of greater diameter than that of opening 26 to insure thatsome of the air from the air supply space 2 will be caused to ow in eachof passages I1, 22. It will be apparent that openings 26, 21 need not bearranged in any particular relation to each other; but it is desirablethat opening 21 be adapted to receive the dynamic pressure of the airflowing in the air supply space 2. In addition, it is desirable thatopening 26 be located as near the upper end of passage I1 as is feasiblein order to cause the air to flow across the surfaces of the insulatorI5.

It will be seen that, since pressure relationships similar to thosedescribed above in connection with the arrangements illustrated inFigures 1-3 will also apply with respect to the arrangement illustratedin Fig. 4, cooling air is caused to ow through passage I1 across thesurfaces of insulating bushing I5 and the exposed end of electrode I3;and that cooling air is also caused to flow through passage 22 and froman annular jet which is discharged against the exposed end portion ofthe solid electrode I3. In this manner both the vulnerable electrodesare cooled and insulated from partly burned fuel particles during thecombustion process. The cooling air also supplies extra oxygen so as toinsure complete combustion in the neighborhood of the spark plug,thereby reducing the amount of unburned fuel in this region which mightotherwise carbonize and be deposited on the comparatively cool surfacesof the electrodes. I have also found that less frequent cracking of theinsulator bushing I5 occurs when cooling is accomplished in accordancewith the invention.

Whereas previously used spark plugs lasted only about ve h-ours inoperation with gas turbine combustors, those incorporating the inventionhave operated as long as 260 hours without serious deterioration. Itwill be seen that the invention provides a simple yet effectivearrangement for cooling both electrodes of an electric igniting deviceas Well as the insulating bushing, and also for preventing fouling bycarbonized particles so that the permissible power rating, operatingtemperature limits, and the time interval between overhauls can beincreased.

While Particular embodiments of the invention have been illustrated anddescribed, it will be apparent to those familiar with the art thatvarious changes and modifications may be made without departing from theinvention, and it is intended to cover in the appended claims all suchchanges and modifications as come within the true spirit and scope ofthe invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. For use in combustion apparatus having a combustion chamber, anigniter including an insulating bushing supporting a first electrodehaving an end portion adapted to project into the combustion chamber, arst wall portion dening a shroud surrounding said projecting end portionand spaced therefrom to define a first annular cooling uid passage, asecond wall portion surrounding said rst wall and spaced therefrom toform a second annular cooling fluid passage, said iirst and second wallsbeing secured at one end to the igniter to form a closure at one end ofboth of said passages, said first wall adapted to cooperate with saidsecond wall at the opposite end to form a second electrode and a nozzlecommunicating with said second passage and spaced from said firstelectrode to define a spark gap, said nozzle being adapted to dischargea jet of cooling and insulating iluid across said `iet and against theilrst electrode to cool both electrodes and to prevent the deposition ofcarbonized fuel particles `thereon, and means for supplying coolingiluid under pressure to both of said passages.

2. Apparatus in accordance with claim 1 wherein the means for supplyingcooling uid to both passages includes an opening adjacent the closed enddened by each of shroud Walls. said openings being of unequal diameterand the second wall portion defining the larger of said openings.

JOHN A. BENSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number

